A double-seat valve with a seat-cleaning function is known from WO 2007/054131 A1 or WO 2007/054134 A1 and US 2009/0008594 A1 or respectively US 2009/0044874 A1 belonging to respective patent families.
In the double-seat valve of the initially named patent family, the independently driven—in relation to a perpendicular normal position—lower closing element, called the first closing element below, comes to rest in a sealing manner in the course of its opening movement on the dependently driven, upper closing element, called the second closing element below, via a middle seal acting between the two closing elements and also transfers the latter to an open position during the further opening movement.
In the double-seat valve of the secondly named patent family, the second closing element has on its end facing the first closing element an opening with a cylindrical circumferential wall, which is flush with a first cylindrical seating assigned to the first closing element, wherein the opening is dimensioned to receive, in a sealing manner during the opening movement, a first end section and a radial first seal of the first closing element before the second closing element opens.
In the double-seat valve of these respective patent families, the first closing element is always designed as a pusher piston with a radially acting first seal. The second closing element is designed either as a pusher piston with a radially acting second seal or as a conical seat plate with an axially/radially acting seal or as an axial seat plate with an axially acting second seal.
The known double-seat valves limit, among other things, the cleaning agent quantity during the respective seat cleaning. Their leakage outlet, which must also divert these cleaning agent quantities into the surroundings of the double-seat valve, is generally measured such that it meets the requirements or respectively regulations of the United States Food and Drug Administration (USFDA) in the “3-A Sanitary Standards for Double-Seat Mixproof Valves, Number 85-02” (hereinafter document [1]), which require among other things that the most minimal passage cross-section of the leakage outlet is to be measured such that it corresponds at least with the passage cross-section of the largest pipeline which can be connected to the double-seat valve (see document [1], requirement D14.2). Furthermore, in connection with the seat cleaning, additional requirements according to document [1] are met, which indicate that the respectively closed seat region is not directly flowed against by the respectively generated seat-cleaning flow or supplied with increasing pressure (document [1], requirement D14.5.2.1) and that the pressure in the closed seat region facing the leakage hollow space must be equal to or less than the atmospheric pressure (document [1], requirement D14.5.2.2).
The known double-seat valves thus also meet further implicit requirements of the aforementioned standards according to document [1], namely those that no cleaning agent may pass through in the case of larger seal defects or even the loss of one of the two seat seals in the course of the seat cleaning of the other closing element via the respective seal defect or respectively the seat region without seat seal. Under these conditions, the known double-seat valves not only meet the requirements for a delimitation of the cleaning agent quantity and avoidance of direct action upon the seat regions in the course of the seat cleaning, but also the requirement for the most turbulence-free possible removal of the seat cleaning flow first into the leakage hollow space and from there into the surroundings, without the respectively closed seat region being flowed against directly or supplied with increasing pressure.
Direct action is understood as any velocity component from the respective seat-cleaning flow directed perpendicularly at the walls delimiting the seat region. It has been shown that any related direct action leads to a conversion of kinetic flow energy into static pressure. Depending on the angle of impact of the flow towards the flowed against wall or body surface, a branching flow with a so-called “branching flow line” results, wherein the later divides the flow into two halves. The branching flow line itself accumulates at the so-called “stagnation point” so that the velocity is equal to zero at this point. The pressure increase as a result of this slowing of the velocity is also called “stagnation pressure.” The pressure-increasing mechanisms shown above generate, if effective, a leakage flow over the respective restriction gap and the defective or the no longer present seat seal.
While the double-seat valves according to the above publications meet the requirements of document [1] solely with flow-mechanical means and modes of action on the components of the double-seat valve bordering the leakage hollow space, DE 10 2007 038 124 A1 or US 2009/0065077 A1 suggests meeting the requirements of document [1] through a separate third element arranged between both closing elements of the double-seat valve and moveable relative to both, a so-called flow barrier element. This flow barrier element shields the at least one sealing element and/or the closing element seat of the other closing element during the venting of the one closing element and during pressurization of the leakage hollow space with cleaning agent, which is located in its closed position, from a direct inflow through the cleaning agent entering the leakage hollow space. According to the description in the latter documents, “shielding” is to be understood in that the sealing element of the respective closing element located in the closed position is not pressurized directly and thus with a high flow velocity by the cleaning agent, wherein it is permitted that the cleaning agent makes its way mainly depressurized and with a low flow velocity into the area of the closing element seat or of the sealing element of the closing element located in the closed position, so that stagnation pressure cannot build up there. According to the description, the flow barrier element does not need to be completely sealed on the housing side; rather, it is preferably spaced from the housing by a small gap. Furthermore, it can be seen in FIGS. 1, 4, 7 and 12 to 15 of DE 10 2007 038 124 A1 or US 2009/0065077 A1 that the leakage hollow space meets the requirement D14.2 of document [1], namely that the most minimal passage cross-section of the leakage outlet is at least equal to the passage cross-section of the largest pipeline which can be connected to the double-seat valve.
An independent third element moveable relative to the two closing elements of a double-seat valve with a seat-cleaning function and guided in a sealing manner in the cylindrical seating for the first closing element is described in WO 98/41786 A1 (page 11, line 24 to page 12, line 9) or U.S. Pat. No. 6,178,986 B1 (column 6, line 58 to column 7, line 11). This embodiment differs from that described in the later published DE 10 2007 038 124 A1 or US 2009/0065077 A1 mainly in the interaction between the third element, the flow barrier element and the associated cylindrical seating for the first closing element. While the older solution provides a seal by means of a radially acting seal in sliding engagement, the third element in the newer solution does not need to be completely sealed on the housing side; rather, it is preferably spaced from the housing by a small radial gap.
It remains to be seen whether the flow barrier element according to DE 10 2007 038 124 A1 or respectively US 2009/0065077 A1 through its “shielding” effect in its embodiment that does not have to be sealed on the housing side or in its sealed embodiment according to WO 98/41786 A1 or respectively U.S. Pat. No. 6,178,986 B1 meets the aforementioned requirement D14.5.2.1 of document [1] and, in the case the corresponding dimensioning of the leakage outlet, also requirement D14.2. Requirement D14.5.2.2 is apparently not met as the flow barrier element now appears within the double-seat valve with a seat-cleaning function in question in a significantly modified embodiment as published in company publication Pentair Südmo Operating Instructions, BAA D 365it Complete PMO, Version 1.01, Double-seat valve type D 365it Complete PMO type D620, published November 2011 (201111) at http://www.suedmo.de/resources/images/790 (hereinafter document [2]).
A flow barrier element designed as an annular body is described in DE 10 2010 046 137 A1, which was published after document [2]. In the ventilation position of at least one of the closing elements, the annular body divides the leakage space into a first leakage space section and a second leakage space section. The annular body is designed such that cleaning agent generated in the respective seat-cleaning position can pass through the annular body from the first leakage space section into the second leakage space section. This passing takes place such that the pressure in the second leakage space section is reduced with respect to the pressure in the first leakage space section and the cleaning agent goes from the second leakage space section to the leakage outlet. Besides the function of the shielding of the seal or respectively of the cleaning member seating of the closing element located in its closed position, the annular body thus also takes on the function of the restriction of the respective seat-cleaning flow. However, this restriction is only possible and sufficient if the annular body is always sealed sufficiently on the housing side and abuts in a sealed manner against the ventilated closing element in the necessary manner.
Through this embodiment, it is possible, as illustrated for example on pages 14 and 25 of document [2] and FIG. 1 of DE 10 2010 046 137 A1 with the first closing element and the pipe shaft connected with it in mind, to reduce significantly the leakage outlet designed in the pipe shaft with respect to the subject matter of DE 10 2007 038 124 A1 or US 2009/0065077 A1 and thus differently from requirement D14.2 of document [1]. This deviating design of the double-seat valve is possible through the exemption clause at D14.2.1.1 of document [1], which states that a leakage outlet reduced with respect to requirement D14.2 is permissible if data is available proving that the maximum pressure between the valve seatings of the double-seat valve is less than or equal to the maximum pressure in a connection line provided with an unreduced leakage outlet between a shutoff valve and a shuttle valve of a comparable arrangement, which is called a “block and bleed” arrangement in document [1].
The double-seat valve according to document [2] or DE 10 2010 046 137 A1 has the noteworthy advantage that the valve housing can be designed one to two nominal widths smaller than the design with a leakage outlet that is not reduced in cross-section and thus in a considerably more cost-effective manner. This is possible because, in the open position of the double-seat valve in which the pipe shaft penetrates the connection opening between the valve housing parts, the passage cross-section of the annular gap between the pipe shaft and the connection opening, which must correspond with the passage cross-section of the largest pipeline which can be connected to the valve housing, can be realized without the above nominal width increase.
However, the double-seat valve according to document [2] or DE 10 2010 046 137 A1 has a big disadvantage in that the third member in the shape of a flow barrier element sealed on the housing side in connection with the other characteristics of its arrangement in the leakage hollow space and integration into the closing element configuration causes a complicated and thus failure-prone structural construction of the double-seat valve. This additional built-in part in the leakage hollow space with additionally necessary sealing means, corners and dead spaces is also generally difficult to clean in the flow and is thus questionable from a hygienic point of view in the proper area of application. A sufficient restriction of the respective seat-cleaning flow is also only ensured when this seat-cleaning flow passes the systematically provided restriction points in the flow barrier element and does not pass in a more or less unrestricted manner in the bypass in the form-fitting connection between the latter and the closing element located in its seat-cleaning position.